This invention relates to an LED (Light Emitting Diode) array, an LED head using the LED array, and an image recording apparatus using the LED head.
An LED (Light Emitting Diode) is used in various ways as a light source for an illumination or a display, or a light source for writing information on a recording medium. For example, an electrophotographic printer uses an LED head including a plurality of LED arrays. Each LED array includes LEDs that emit red (i.e., a single color) light arranged along a plurality of rows in a scanning direction. The image recording apparatus is configured to control the LED head to expose a photosensitive body, and superimpose toner images of a plurality of colors on a recording sheet, so that a color image is formed on the recording sheet.
Further, there is known an image recording apparatus that directly irradiates a photosensitive film or a photosensitive sheet with lights of a plurality of colors. For example, such an image recording apparatus is configured to receive a memory card storing digital image data (obtained by a digital camera or the like) inserted therein. Further, the image date is supplied to the LED head including a multicolor LED array that emits lights of a plurality of colors. In accordance with the image data, the multicolor LED array emits lights of the respective colors on the photosensitive sheet or the like.
An example of a conventional multicolor LED array that emit lights of a plurality of colors is disclosed in, for example, Japanese Laid-Open Patent Publication No. 8-64862 (i.e., U.S. Pat. No. 5,424,560). The LED array disclosed in the publication has a structure including a red LED organic layer patterned on an electron transport layer, a green LED organic layer covering the red LED organic layer and the electron transport layer, and a blue LED organic layer covering the green LED organic layer and the electron transport layer. Transparent electrodes are formed above contact portions where the respective LED organic layers contact the surface of the electron transport layer. Red, green and blue lights are emitted from the contact portions where the respective LED organic layers contact the surface of the electron transport layer. Therefore, the light emitting positions of the respective colors are different from one another in height.
Since the light emitting positions of the respective colors are different from one another in height, the distances from the respective light emitting positions to the surface of the photosensitive material (such as a photosensitive sheet) are different from one another. Thus, it is difficult to focus all of the lights of the respective colors on the surface of the photosensitive material, and therefore it is difficult to form a sharp image.